Earlier quoted context omitted.
"A good programmer is someone who always looks both ways before crossing a one-way street." -- Doug Linder
"Three programmers come to a one-way street. The academic looks to the right, doesn't see any oncoming cars, and crosses. The corporate programmer looks to the left, then looks to the right, and then crosses. The distributed systems engineer looks to the left, then looks to the right, then looks up to make sure there aren't any planes falling out of the sky…"
The distributed systems engineer definitely uses a mirror to watch both directions at the same time while crossing the street. They've been caught by Time of Check - Time of Use errors before.